1. Field of the Invention
This invention relates to electric arc welding and, more particularly, to electric arc welding using a continuous arc with inert gas shielding.
2. Prior Art
This type of welding, i.e., electric arc welding with inert gas shielding, is well known in the prior art. It is often referred to as a continuous welding process and is generally used for welding continuous forms. The restriction in use of this type of welding stems from the fact that the noise produced by the high frequency HF current used to initiate the arc for this type of welding, when used for welding non-continuous members, runs almost continuously and generates noise that exceeds the level prescribed by the Operational Safety and Health Act, hereinafter called OSHA.
As is well known to those skilled in the art, OSHA is the National Agent which regulates noise level in industrial plants and factories. Generally, the regulation is such that the noise is kept below the level where it will damage human hearing. In a recent directive issued by OSHA, noise level has to be equal to or less than 85 decibels (i.e., .ltoreq.85 dba). If the noise level exceeds this standard, workers in the vicinity of the noise creating means must wear hearing protection or the noise producing means must be contained within a sound proof enclosure.
Whenever the TIG process is used for welding continuous forms, the noise which is generated by the TIG welder is within the noise level prescribed by OSHA. However, when this process is used for welding non-continuous forms the noise level generated by the HF starting current exceeds the OSHA requirement. In order to satisfy the OSHA standard, the user must resort to either sound proofing or equip workers in the vicinity of the welder with hearing protection. Either approach significantly increases the cost to the user which, in turn, increases product cost. As a result, this type of welding is not used.
In order to appreciate and understand the noise problem created by the TIG process, a synopsis of the TIG welder operation will be given. Generally, a TIG welder incorporates two separate and distinct circuit systems, a high frequency start circuit and an AC or DC circuit. The function of the HF circuit is to initiate the welding arc. Once the arc is initiated, the welder automatically switches and runs on the DC or AC circuit.
As is well known to those skilled in the art, the high frequency circuit is a noise producing circuit. In fact, the noise created by the high frequency circuit is outside of the range prescribed by OSHA. However, this circuit is operational only momentarily, i.e., to initiate the welding arc, and, therefore, the human ear does not recognize the noise. As such, the OSHA standard is not violated. Once the arc is initiated, it will remain continuous if welding is done on a continuous form. The arc is continuous and it is sustained by the DC or AC circuit in the welder. As was stated, the DC or AC circuit produces a low level noise which is within tolerable levels.
However, if the welding is done on a non-continuous form or on an intermittent surface, the welder is always operating in the start mode which is noise producing. Stated another way, in welding an intermittent surface or form the high frequency circuit initiates the arc. However, before the running of the welder is transferred to the control of the DC or AC circuit, the arc is lost. As such, the system is forced to run in a start mode and produces intolerable noise.
In addition to the noise problem discussed above, the weld joint which is produced by the welder when it is running on the high frequency circuit is less than satisfactory and separates quicker than a joint which is formed by the welder when it is running on the DC or AC circuit. This result stems from the fact that when the system is running on the DC or AC circuit there is a steady flow of electrons, for a sufficient time, from the welding electrode to the members to be welded to create a homogenious joint. However, when the welder is running on the high frequency circuit, the flow of electrons is intermittent, which results in the creation of an unsatisfactory weld joint due to crystalization.